She didn't choose to seduce him, she caught feelings.
Look, the explanation would never meet the vitriol that has been spewed at Steph (which I feel quite a lot of responsibility for since I am the anti-steph club leader). There's nothing Drifty could have done that would satisfy everyone. However, as it is his story (and we all are choosing to play his game) we need to accept the explanation as logical within his world. In our world the entire thing wouldn't make sense, I could nitpick the entire concept to death (and some may wonder why I would spare Drifty when I've nitpicked other games much more - because I'm an arbitrary motherfucker) but the fact is that, if I want to enjoy the game, I need to trust in the story that Drifty is sharing with me (us).
I think that including Steph in the group of friends will make for a more interesting story than excluding her. Because, as Drifty has said, that is going to be the original story he'd created. I don't want to play the edited story that he had to come up with after the many knee jerk reactions that the initial release received (I am definitely one of those first jerks that responded unfavorably to being forced to have sex with Steph, that experience helped me learn I really don't like games that don't allow me to choose who the MC fucks). Do I like Steph? Not really, she made a choice to hide information from James, but I am willing to move on from the anger that I originally felt because we have an explanation now. James deserved one, he got one, now he can continue to try and help all of his dysfunctional friends (and himself) move onto a healthier perspective/life.
To continue to dwell on Steph, what she did, her explanation, etc... It's not healthy for James or for the players. People need to make a simple choice, let it go and continue to play a great game with an engaging story or move on from the game.